Professor of Environmental Health Sciences, Micaela Martinez, gathered data for 69 infectious diseases from the U.S. Centers for Disease Control and Prevention, the World Health Organization and peer-reviewed journal articles. She then mapped the time of year when outbreaks tended to occur, ranging from common infections to rare tropical diseases.

As reported in the journal PLOS Pathogens, she found that in a given year, flu outbreaks occur in the winter, chicken pox in the spring and polio and gonorrhea in the summer.

The study describes four main factors that drive the seasonal influence on disease. Seasonal flu is influenced by environmental factors such as humidity and temperature and in vector-borne diseases such as Zika, the environment affects the proliferation of mosquitos.

Host behaviours also play a role; children being in close proximity during the school year, for example, is a factor involved in the spread of measles.

Ecological factors are also involved. For example, the bacteria that causes cholera is maintained in water that is supported by algae.

Being aware of such drivers of seasonal outbreaks could help public health officials intervene to prevent the spread of disease. They could introduce a strategy to target the survival of cholera-causing bacteria in bodies of water filled with algae, for example.

Another potential factor in diseases such as polio is seasonal biological rhythms like the ones that control animal migration and hibernation. However, this possibility requires further research.

Martinez says seasonality is a powerful and universal feature of infectious diseases but is something that the scientific community has largely ignored when considering the majority of infections.

“Much work is needed to understand the forces driving disease seasonality and understand how we can leverage seasonality to design interventions to prevent outbreaks and treat chronic infections,” said Professor Micaela Martinez, Study Author.